As more and more people move to urban environments, there is an ever increasing need to provide a clean air environment at home and in the work place. In urban areas, where polluting levels sometimes exceed maximum values set by the EPA. The need for a clean air environment becomes even more apparent. In view of the posed hazards of these excessive pollutants, the public has demanded a means for removing such pollutants so as to provide a healthy environment for both living and working. Furthermore, many of these particles in the air can act as irritants and/or increase or aggravate people's allergies. Air born pollutants can also contribute to respiratory infections and illnesses which can be hazard to individuals with respiratory problems. Particles in the air may create problems with burning eyes, act as nose and throat irritations, contribute to headaches and dizziness and can result in coughing and sneezing. Furthermore, these particles may include various types of spores, bacteria, viruses or harmful particles which may cause serious illness to a person.
In an effort to reduce such irritants and/or harmful particles, many family homes and offices have incorporated a central filtering system to remove particles entrained in the air. Unfortunately, these systems are very expensive and/or do not remove many of the small particles which can be the most hazardous and irritable to persons such as spores, bacteria, virus and some harmful chemicals. Typically, these filtering systems only remove about 300,000 particles out of about 20 million particles which flow into the filter medium. The small particles which make up a majority of the particles in the air freely pass through conventional filters.
Specialized filters have been developed to remove very small particles. Such filters are known as HEPA filters which stand for High Efficiency Particle Air Filters which, by government standards, are filters with a minimum efficiency of 99.97%. The industry defines HEPA filters as those filters which are efficient in removing 99.97% of the air born particles of the size of 0.3 micron or larger. Such filters are used in ultra clean environments such as in a laboratory, in electronic and biologically clean rooms, in hospitals and the like. These filters have recently been incorporated in air filters for business and individual use.
In U.S. Pat. No. 4,629,482, a portable HEPA room air purifier, is disclosed. The purifier incorporates a cylindrical HEPA filter and the filter is mounted within the filter housing having an annular discharge at its base. A centrifugal fan is incorporated in the housing to draw air through the filter and discharge air at the base of the housing. Due to the configuration of the purifier, it is necessary to space the base of the apparatus from the main housing. Such a configuration also requires that the apparatus be designed somewhat larger than some consumers may desire. The discharge of the air at the base of the unit results in the recirculation of particles which had settled out onto the floor. Such recirculation of settled particles places more particles in the room, which can increase particle irritation. The purifier does not incorporate a gas filter to remove irritable or noxious gas from the air.
In U.S. Pat. No. 5,435,817, another type of portable HEPA room air purifier is disclosed. This unit is cylindrical in shape and includes a base discharge. A centrifugal fan is incorporated to draw air into the top of the unit and discharge filtered air at the base of the unit. The unit incorporates an outer deflector wall to radially discharge air at the bottom of the unit, such that the exhaust air is channeled generally circumferentialy about the base of the unit. The discharged air at the base of the unit results in the redistribution of settled particles back into the air. The purifier is also absent any mechanism for removing unwanted gases in the air.
The efficiencies of HEPA filters are all based upon 0.3 micron size particles. Historically, it was believed that such particles were the most difficult to remove from the air. However, recent particle filtration testing has shown that particles the size of about 0.1 micron are the most difficult to remove from the air. Standard HEPA filters do not efficiently remove such small particles and allow such particles to freely pass through the filter medium. An analysis of these small particles has shown that the particles do not naturally fall out of the air, but instead maintain entrained in the air by constantly bouncing off of other particles in the air (i.e. Browning effect). These small particles also have been found to deviate from the air flow thus making such particles even more difficult to remove from the air.
In view of the foregoing, it has become necessary to overcome the physical determents of prior art portable filter structures by providing a compact portable unit which filters particles as small as 0.1 micron out of the air, filters the air without re-circulating particles which have previously settled out of the air and removes undesirable gases from the filtered air.